Nucellar embryo culture of Citrus sinensis L. and Citrus limon L.

Nucellar tissue cultures of polyembryonic Citrus sinensis cultivar Valencia Late and Citrus limon cultivar Rough Lemon produced somatic embryos within 60 days of culture on Murashige and Skoog (MS) basal medium supplemented with 0.4 g l-1 of filter-sterilised casein hydrolysate or 10% coconut water. Embryos that were separated and subcultured in MS media containing casein hydrolysate or coconut water but without hormones, first developed roots within 4 to 8 months and then shoots within 6 to 9 months of in vitro culture. Plantlets were transplanted to soil from 7 to 9 months after initiation. Callus-like tissue consisting of pseudobulbils was observed after 4 to 5 months from the time of initiation. Pseudobulbils developed into visible embryos with multiple cotyledons when subcultured into MS media containing casein hydrolysate or 10% coconut water after 19 to 27 days of in vitro culture. These embryos produced plantlets in which roots developed after 6 to 10 months and shoots formed after 8 to 11 months from the time of initiation. Key Words: Citrus, nucellar embryo culture, somatic embryogenesis (African Crop Science Journal: 2000, 8(2): 109-116

Efficacy of thidiazuron in In vitro propagation of carnation shoot tips: Influence of dose and duration of exposure

One of the main challenges facing production of good quality cut flowers is the lack of clean planting material especially among resource poor farmers who resort to multiplying their own propagules with detrimental results. Carnation (Dianthus caryophillus   L. cv. Yair) is an important export crop among farmers in Kenya. Carnation production, however, is constrained by lack of clean planting materials. The main objective of this study was to evaluate the potency of thidiazuron (TDZ), a phenyl urea, in evoking morphogenic response in vitro compared to combined auxin (NAA) and cytokinin (kinetin) from shoot tip explants of carnations as one possibility of producing en mass clean planting materials. In addition, the study was instituted to determine the optimum concentration and duration of exposure of TDZ in the number, length and general quality of shoots formed. Results from the study indicate that TDZ, at low concentrations of 0.1-1 μM, was just as effective as 0.2 mg-1 L NAA + 0.2 m-1 L kinetin in improving the number, length and quality of shoots regenerated from the explants cultured in vitro. Although multiple shoots were formed from explants cultured on media supplemented with high doses of TDZ (5 μM), they were dwarfed and of a poorer quality. Prolonged exposure of carnation shoot tip explants to high concentrations of TDZ was detrimental to plant regeneration. Sufficient morphogenic response could be achieved by exposing the explants to 1-5 μM TDZ for short durations of 3-10 days with subsequent transfer to MS basal medium devoid of any plant growth regulators